The main objective of the proposed research is to study with the light and electron microscope the connections and ultrastructural organization of the visual thalamus and cortex, with the goal of understanding the anatomical bases of the neural integrations which take place in these areas. This research relies on a number of techniques for tracing nerve pathways including anterograde degeneration and anterograde and retrograde axonal transport. In one series of experiments, the synaptic organization and sources of afferent connections are being analyzed in a thalamic relay nucleus concerned with visual functions, the pulvinar. In particular we are interested in how various inputs converge in the synaptic complexes in this area. In a related series of experiments we are studying how the synaptic complexes in the pulvinar develop when a major source of its input, the superior colliculus, has been removed and an anomalous projection from the retina has been induced to enter it. A series of experiments also is being conducted on area 18 in the neocortex, a region in which a number of inputs including the contralateral hesmiphere, the ipsilateral area 17, and the pulvinar converge. We plan to compare these inputs in terms of their laminar distribution and their pre- and postsynaptic processes. In a final series of experiments the cells of origin for each of the efferent pathways of the superior colliculus are being identified by injecting horseradish peroxidase in each tectal target. These cells are then characterized in terms of the morphology and laminar distribution of their dendritic fields in Golgi impregnated material. This information is then correlated with existing information concerning the laminar distribution of afferent connections of the superior colliculus.